science fiction involving extraterrestrials, after 1940

Alien invasion and subversion became popular themes in American and British
(though not Russian) science fiction during the Second World War and the
Cold War years that followed (see Cold War,
linked to UFO reports). John W. Campbell's
"Who Goes There?" served as an inspiration for many subsequent tales of
aggressive extraterrestrial monsters and shape-shifters, both in print and
film. Paranoia and the fear of loss of self-identity, engendered both by
the perceived communist threat and the reactionary right-wing excesses of
McCarthyism found ample expression in the alien motif. Robert Heinlein's
The Puppet Masters, for example, envisages slug-like parasites which
fasten themselves to their victim's back and thereafter assume control over
the person's body and brain. The idea of individuals being "taken-over,"
or invasion by insinuation, also underlies Jack Finney's The Body Snatchers,
better known for its two cinematic interpretations in Invasion
of the Body Snatchers. The postwar years, however, also saw further
exploration of the more optimistic concept of advanced extraterrestrials
as facilitators of future human evolution. This became a favorite theme
of Arthur C. Clarke, as exemplified in his
short story "The Sentinel" – the inspiration for 2001:
A Space Odyssey – and Childhood's
End. As for the aliens themselves, portrayals of their possible
forms, habitats, behaviors, and minds, became ever more adventurous and
diverse. James White's Sector General stories, set in a huge space-station/hospital
on the Galactic rim, ingeniously and humorously depicts the medical dramas
that accompany the treatment of all manner of exotic species, while Hal
Clement, Larry Niven,
and Robert Forward were among those to speculate
on life in the most unexpected and bizarre locations. Other writers, such
as Stanislaw Lem and Ray Bradbury,
used aliens as a means of throwing into sharp relief humanity's own strengths
and weaknesses. The consequences of first contact
were also investigated, by Fred Hoyle, James
Gunn, Carl Sagan, and others, often leading to
disquietening conclusions.